This invention is generally directed to a unique development system, and more specifically, the present invention is directed to an improved apparatus for charging and transporting toner particles to a charging zone situated between a metering charging means such as a metering charging roll and a transporting means. In one embodiment, the present invention is directed to an apparatus and process for simultaneously metering and charging insulating toner particles to a positive or negative polarity, by delivering these particles with a charging brush means, into rubbing contact with a metering charging means, such as a metering charging roll, wherein the toner particles are further charged to either a positive or negative polarity. The brush means contained in the apparatus of the present invention accomplishes a number of operations including, for example, its primary function, that is for transporting toner particles contained in a reservoir or sump, to the metering charging roll nip present in the apparatus involved. Moreover, the brush functions in a manner so as to apply charges to the toner particles contained in the sump in view of the triboelectric relationship between the bristles of the brush means and the toner particles, and further the brush can function as a cleaning mechanism whereby residual toner particles remaining on the donor roll are removed therefrom by the brush which is in contact therewith. Also, the charging brush means which is moving in either a clockwise or counter-clockwise direction, causes the mixing of toner particles contained in the reservoir or sump apparatus.
The development of images by numerous methods, including electrostatographic means is well known. In these systems, toner particles are deposited on an electrostatic latent image contained on an insulating surface such as selenium, using for example, cascade development, magnetic brush development, powder cloud development, touchdown development and other development systems. Generally in these systems two component developer compositions are selected for causing development, that is compositions containing toner particles and carrier particles. As it is known that there are a number of disadvantages associated with two component systems, including additional costs and processing equipment, there has been considerable effort directed to designing systems which utilize toner particles only. Generally, these systems allow the elimination of a developer reservoir, a toner dispenser, and a toner concentration control means.
Single component development systems are also known, that is, developer compositions comprised of toner resin particles only. The imaging device currently in use generally consume these conductive toner particles, whereby imagewise toner deposition onto the imaging member is obtained by induction toner charging. Electrostatic transfer of conductive toner particles to plain paper is however usually inefficient, that the charge of the toner particles can be reversed by induction charging with plain conductive paper. Electrophotographic systems using conductive single component toner particles therefor usually require a special overcoated paper to achieve electrostatic transport. Moreover, in single component development systems containing conductive toner particles it is difficult to control undesirable background, and background suppression cannot be achieved as the toner particles are inductively charged, and deposited on the image bearing members, which is not the situation in two component development systems wherein the control of background development is accomplished by an electrostatic force acting on the triboelectrically charged toner particles, causing such particles to be directed away from the imaging member.
There is disclosed in U.S. Pat. No. 3,900,002 development systems for developing latent electrostatic images which include a rotating fur brush, the purpose of which is to deliver toner particles to the imaging member. As illustrated in FIG. 1 of this patent, a cylindrical applicator, such as a natural fur brush is selected for incorporation into the apparatus. A similar disclosure is presented in U.S. Pat. No. 3,929,098 wherein there is selected for electrostatic development a brush contained in a developer sump, which brush transfers toner particles to a donor roll. Particles contained on the donor roll are subsequently provided to the photoreceptor imaging member.
There is disclosed in U.S. Pat. No. 3,638,613 a developer apparatus wherein a transfer or donor roll triboelectrically attracts to its surface toner particles contained in a sump or reservoir. Apparently in this apparatus the fur brush is used for the purpose of removing toner particles from the transfer or donor roll and depositing these particles upon a charged surface where the image contained thereon is rendered visible.
Other patents are in existance which disclose the use of various rolls including fur brush rolls for transporting toner particles to various stations in the electrostatographic imaging apparatus. While a similar roll or brush is selected for incorporation into the apparatus of the present invention and while this roll may perform some of the same functions as the prior art rolls, it is the combination of such a roll with a metering charging roll means that the present invention envisions, which combination is not disclosed in the prior art.
There is disclosed in U.S. Pat. No. 4,459,009, the disclosure of which is totally incorporated herein by reference, an apparatus and process for simultaneously metering and charging non-magnetic insulating toner particles, which apparatus comprises in operative relationship a means for simultaneously metering and charging non-magnetic insulating toner particles, a means for transporting the toner particles, a means for supplying nonmagnetic insulating toner particles to the transporting means, a means for applying a bias to the metering charging roll means, a means for applying a bias to the transport means, a means for removing toner particles from the metering charging roll means, wherein toner particles are charged to the appropriate polarity and magnitude in a charging zone situated between the metering charging means and the transport means. The apparatus as described in the co-pending application is sufficient for its intended purposes, however, one disadvantage associated with such an apparatus relates to transporting an appropriate supply of toner particles to the charging roll nip when the apparatus assumes certain configurations in an imaging device.
There thus continues to be a need for improved processes and apparatus for the development of latent electrostatic images wherein improved quality of development is obtained, and which apparatus are efficient, simple in design and economical. Moreover, there continues to be a need for improved single component imaging systems where insulating non-magnetic and colored toner particles are appropriately charged and there is obtained two-component image quality utilizing a single component development method, apparatus and insulative single component toner particles so as to enable the efficient electrostatic transfer of such particles to plain paper, and where there is included in the apparatus a brush means for the primary purpose of pre-charging toner particles contained in a developer sump and transporting these toner particles to a charging nip situated between a metering charging roll and toner transporting means. Additionally, there continues to be a need for improved processes and apparatus wherein single component toner particles are metered onto a transporting member and simultaneously rapidly charged to the desired polarity. Further, there is a need for the provision of an apparatus and process wherein background development is substantially controlled and eliminated by electrostatic forces, and wherein the reliability of the system hardware and materials is increased, which apparatus includes therein a brush means for the primary purpose of pre-charging and mixing the toner particles and transporting these particles to a charging nip. Additionally, there continues to be a need for an apparatus and process which will allow the uniform development of both fine lines and large solid areas of an electrostatic latent image while obtaining minimum background density and wherein the apparatus can be incorporated into a xerographic imaging device in a number of different configurations.